1. Field of the Invention
This invention is in the field of transport devices employing picker means which are arranged to pick up a plurality of parisons from an oven in which they are heated to a blow molding temperature and transport them rapidly to molds where the blowing operation takes place. The invention features an automatic system which enables preselection of the spacing between the plurality of parisons to make it possible to vary the spacing between the parisons for various reasons in their transport from the oven to the molds.
2. Description of the Prior Art
While there are many different types of blow molding processes used, there are three steps which are included in all. First, there is the formation of a hollow tube of molten resin known as a parison. Next, the parison must be positioned between mold halves, and finally, the parison is blown with compressed air so that it takes the shape of the mold.
The temperature of the parison at the time of blow molding is quite critical to achieve the best results. Therefore, there must be provided an efficient and rapid transport system between the oven in which the parisons are being continuously heated, and the mold system in which they are to be blown. Transfer of the parison to the mold system by means of grippers has the advantage of being mechanically simpler than moving the massive molds to and from the ovens. However, this advantage may be offset by the fact that the parisons have increased time to sag and become chilled during transport.
In one commercial system presently being employed, a conveyor consisting of a roller chain is used for transporting parisons through the heating oven. The spacing of the parisons is controlled by the pitch of the chain, since the parison carrier is attached directly to the chain. With a chain pitch, for example, of 1 inch, the picking must occur in multiples of a double pitch, i.e., at 4 inches or 6 inches, or more. Thus, cavity spacing can be as little as 4 inches which in some cases is too small, or 6 inches which may be too wide.